Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$77.87	9.385%	$85.1781	$85.18	$85.20	$85.20
Purchase #2	$5.74	9.693%	$6.2964	$6.30	$6.30	$6.30
Purchase #3	$141.85	10.176%	$156.2847	$156.28	$156.30	$156.30
Purchase #4	$174.82	9.545%	$191.5066	$191.51	$191.50	$191.50
Purchase #5	$81.59	13.266%	$92.4137	$92.41	$92.40	$92.40
Purchase #6	$137.42	6.569%	$146.4471	$146.45	$146.45	$146.40
Purchase #7	$183.27	12.367%	$205.935	$205.94	$205.95	$205.90
7 purchase totals =	$802.56		$884.0616	$884.07	$884.10	$884.00